The invention relates to an apparatus for production of nanosized particulate matter by vaporization of solid materials. Vaporization takes place by material ablation obtained through application of an electric field and consequent generation of an electrical discharge between two electrodes at least one of which is embodied by the material to be vaporized.
As known, ablation is removal of surface atoms from a solid following localized transferring of an energy pulse to a region thereof, and it results in local vaporization of such a region.
Usually energy transferring takes places in a sufficiently quick manner so that transformation of the concerned material portion can be considered as occurring under adiabatic conditions, i.e. without the remaining material being affected by heat and in such a manner that the remaining material is maintained at a much lower temperature than its boiling temperature.
In addition, since surface atoms alone are subjected to ablation, material extraction from the solids takes place without running the risk of possible remelting of the material submitted to ablation.
In addition, the adiabatic feature of the process enables highly refractory materials such as graphite, molybdenum, tungsten to be vaporized. This aspect is of particular relevance for gas-phase synthesis of a wide variety of materials: metals, oxides, carbon, carbides and nitrides.
It is also known that for nanoparticles production not only vaporization of solid materials is to be carried out, but also condensation to nanosized particles of the vaporized solid material. This cooling takes place in a thermal bath or cooling element generally consisting of an inert gas.
The energy pulse causing ablation is transmitted to the solid to be vaporized through two mutually alternative modalities: through generation of an electrical discharge or through laser radiation.
In connection with the second modality, it is known that sources or vaporizers for nanoparticle production through laser radiation comprise an excimer laser generating a laser pulse. The pulse is such directed that it strikes on a target to vaporize a small portion of same.
A drawback of these sources or vaporizers is the following: lasers cannot transfer an energy intensity onto a target which may be sufficient for any application, i.e. sufficient for any type of material to be vaporized.
In addition, for control of the laser beam section and the laser beam focusing degree on the target, use of very delicate optical systems to be made from high quality special materials is required.
Furthermore, said lasers for vaporization are by themselves very expensive systems of complicated management and low efficiency.
They are also of difficult adjustment, i.e. they can be hardly adapted to different production or work levels.
In connection with the first modality, i.e. energy transfer by application of an electric field, electric arc vaporization sources are on the contrary used, in which ablation of the solid material takes place following an electrical discharge fired between the electrodes.
Through an appropriate feeding circuit a potential difference is in fact applied to the two electrodes so that a voltaic arc is stricken between them: the electrical discharge causes a small material ablation from either of the electrodes.
The two electrodes are inserted in a block of non-conductive material so that firing of the discharge is always constrained in the gap between the two electrodes. A gas pulse is further constrained to run within the channel delimited by the two electrodes. The high-pressure gas passing during the discharge has the function of removing the ablated material which can thus be used for production of nanoparticles and possibly formation of molecular beams.
Drawbacks in this type of sources are represented by a poor stability of same and the need for frequent servicing because the ablation mechanism causes formation of a deposit on the electrode facing the one from which the material is extracted and/or the walls of the channel in which the electrodes are inserted. This involves a continuous and progressive modification of the gap between the electrodes (and, as a result, instability and short operation life) until a short-circuit occurs.
The technical task underlying the present invention is therefore to provide an apparatus for production of nanosized particulate matter overcoming the mentioned drawbacks present in known systems.
Within the scope of this technical task it is an important aim of the invention to devise an apparatus provided with features such as stability and intensity which are crucial from the point of view of application.
Another important aim is to devise an apparatus of simple and cheap construction.
The technical task mentioned and the aims specified are achieved by an apparatus for production of nanosized particulate matter by vaporization of solid materials comprising: at least one first chamber, at least one vacuum pump connected with said first chamber, a body inserted in said first chamber, a cavity formed in said body, means for feeding a gas flow to said cavity, at least one anode and at least one cathode at least partly inserted in said cavity, said cathode consisting of material to be vaporized, a power supply to apply a voltage between said anode and cathode and to generate an electrical discharge, and a nozzle communicating with said cavity and adapted to convey a beam of particles consisting of vaporized material from said cathode, in said apparatus said cathode facing said gas flow, so as to intercept the latter, and said anode and cathode being positioned so as to allow a propagation of said electrical discharge to said gas flow and ionization of said gas.